JP2014028382A - Bending method of metal pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bending method of an inexpensive thin wall pipe having high work accuracy or a metal pipe capable of small bending work of a flexural center radius, for pressing a bending part by four-point support, by using a bending metal mold, a cushion metal mold, and a movable roll.SOLUTION: A processed metal pipe is placed on a cushion metal mold and a pair of movable rolls arranged on its both sides, and a bending work is executed by pressing the bending metal mold to the processed metal pipe from just above the cushion metal mold. Tension is generated in a bending part of the metal pipe from frictional force Fand Fof a pipe outer surface by a cushion load and a roll load, and the bending work is executed while relieving compressive stress of a bending center part, and occurrence of buckling can be restrained thereby.

Description

  The present invention relates to a bending method of a metal pipe used for transportation equipment such as automobiles, machine parts, or construction members.

Although the metal tube provided for the above-mentioned use may be used as it is straight, it may be used after being appropriately bent.
As a method for bending the metal tube, for example, as shown in FIG. 1A, a method is generally used in which one end of a metal tube to be processed is fixed to a bending die, and the bending die is rotated to perform bending. (For example, Non-Patent Document 1). In addition, as shown in FIGS. 1 (b) and 1 (c), a three-point bending method is adopted in which the base tube is fixed with two support rolls or a support die, and a bending die is pushed into the center to bend the metal tube. (Also non-patent document 1).

  Further, as a method of bending a metal tube by pushing a bending die, Patent Document 1 proposes a method in which two support rolls are made movable and the bending die is pushed and bent at the center thereof. Since the two support rolls are separated from each other in accordance with the movement of the bending mold, the distance between the fulcrums of the bent part (distance between the two rolls) is shortened and the rigidity of the pipe bent part is increased. It is intended to provide a bending method in which buckling is unlikely to occur as compared to the press bending method.

  Furthermore, in Patent Document 2, a roll is used in which a bending die is lowered with respect to a cushion die, a metal tube is sandwiched and a press load is applied, and at the same time, a metal tube is sandwiched in the bending die on the side of the cushion die. Then, a press bending method for bending is proposed. In this press bending method, since bending is performed by holding the metal tube in the cushion mold and at the same time as the bending mold is lowered, it is sandwiched between the bending molds with a roll. Is possible.

“Tube Forming” pages 36-64 (published by Corona on October 30, 1992)

JP 2007-307615 A JP-A-4-251615

The rotary drawing and bending method shown in FIG. 1 (a) uses a wiper that is a mold for suppressing wrinkles, a side booster and a back booster for suppressing breakage, and a mandrel for suppressing flattening. t / D is 5% or less) and is suitable for bending with a small bending center radius. However, since the number of molds to be used is large, it takes time for setting, and it is necessary to prepare a mold suitable for the dimensions of the metal tube. Moreover, since the apparatus itself is expensive, the manufacturing cost increases.
In addition, the press bending method shown in FIGS. 1 (b) and 1 (c) uses three points: a bending die and two support dies (support roll or support die). Simple and inexpensive. However, in the press bending method, the bending die is pushed into the metal tube and bent, so that the bending stress acting on the bending portion increases, and the bending inner portion tends to buckle. In particular, when a thin tube or a bending process with a small bending center radius is performed, the rigidity of the metal tube is lowered and the bending stress generated at the bending portion is further increased, so that the possibility of buckling is further increased.

In the press bending method in which the two rolls proposed in Patent Document 1 are movable, buckling is less likely to occur. However, as in the conventional press bending method, the thin tube or the bending center radius is reduced. When a small bending process is performed, a small gap is generated between the two movable rolls, so that the bent portion is buckled and bending is difficult.
Further, even in the press bending method using the roll proposed in Patent Document 2, the bending process is performed while the metal tube is sandwiched between the cushion mold and the bending mold, so that the bending angle of the bending portion is larger than 90 °. Becomes difficult. In addition, the bending portion is restricted by three-point support by a bending die, a cushion die, and one roller, so that as the metal tube becomes thinner and the bending center radius R becomes smaller, buckling occurs inside the bending. It tends to occur.

  The present invention has been devised to solve such problems, and is based on a press bending method in which the apparatus is simple and the processing time is short, and a thin-walled tube (t / D is 5% or less, t Is the thickness of the metal tube, D is the outer diameter of the metal tube), or a bending mold, cushion mold, which can be bent with a small bending center radius (R / D is 3 or less, R is the bending center radius), The object of the present invention is to propose a low-cost and high-precision processing method for bending metal pipes, which uses a movable roll to press the bent part with four-point support.

In order to achieve the object, the metal pipe bending method of the present invention places a metal pipe to be processed on a cushion mold and a pair of movable rolls arranged on both sides of the cushion mold, and the bending mold is directly above the cushion mold. The mold is pressed against the metal pipe to be processed and bent.
Each of the bending mold, the cushion mold and the pair of movable rolls is bent while restraining the metal pipe to be processed or applying a load for bending.

As a pair of movable rolls, a bending mold, a cushion mold, and a pair of movable rolls, each of the metal pipe contact surfaces to be processed has a width greater than the diameter of the metal pipe to be processed and a depth greater than the radius of the metal pipe to be processed. It is preferable to use one having a circular cross-sectional groove. In addition, these bending molds, cushion molds, and a pair of mobile rolls include a bending mold and a cushion mold, and / or a circular arc length of a groove portion that combines a bending mold and a mobile roll. It is preferable to use one having a length not longer than that.
Furthermore, during actual bending, depending on the processing conditions such as the dimensions of the metal tube and the bending center radius, bending can be performed with a restraint material such as steel shot, sand, or beads inserted into the metal tube as a wrinkle suppression method. preferable.

In the method for bending a metal tube provided by the present invention, press bending is performed by supporting the bending portion of the metal tube at four points. For this reason, a thin-walled tube (t / D is 5% or less) that is easily generated by a press bending method in which the conventional metal tube is supported at three points, or bending with a small bending center radius (R / D is 3 or less). ) Can be suppressed.
Moreover, since the base of the metal tube bending method provided by the present invention is a press bending method, the processing apparatus is inexpensive, the processing setting is simple, and the processing time is short.
Therefore, according to the present invention, a thin tube (t / D is 5% or less) or a bending process with a small bending center radius (R / D is 3 or less) can be performed with excellent processing accuracy and at low cost. Become.

The figure explaining the general bending method of a metal pipe The figure explaining the press bending method by the three-point support using a movable roll The figure explaining the press bending method by the four-point support using a movable roll A diagram for explaining the deformation process at each time point during 4-point support press bending (part 1) Drawing explaining the deformation process at each time point during 4-point support press bending (Part 2) The figure explaining the metal mold shape when performing 4 point support press bending

  As described above, in the press bending method using a movable roll with three-point support, buckling may occur at the bending center portion in the initial bending stage where the bending angle θ is 0 <θ ≦ 30 °. This is because, as shown in FIG. 2, there is a gap between the two rolls, the rigidity of the bending center of the metal tube is low, and the bending stress of the bending center is the largest in press bending. This is because buckling is likely to occur at the center of bending.

Therefore, in the present invention, as shown in FIG. 3, a cushion mold is installed in the bending center portion to fill a gap between the two movable rolls, thereby increasing the rigidity of the metal tube bending center portion. . In addition, since the tension due to the frictional force F1 outside the tube due to the cushion load and the frictional force F2 outside the tube due to the roll load is generated in the bending portion by installing the cushion mold, the compressive stress inside the bending is relieved.
By improving the rigidity of the metal tube bending center portion and generating tension in the bending portion, it is possible to suppress buckling that is likely to occur in the initial bending stage where the bending angle is 0 <θ ≦ 30 °.

  Further, when the bending angle is 30 ° or more, the bending process at the bending center part is completed, so that the bending stress at the bending center part is reduced, and a process that does not buckle at the bending center part becomes possible. For this reason, a bending process without buckling is possible by pressing the pipe into the bending mold with a movable roll while the metal pipe is sandwiched between the bending mold and the cushion mold. Moreover, since the tension | tensile_strength of the axial direction of a metal pipe can be enlarged by making the groove shape of a movable roll below into the dimension of a metal pipe, buckling can be suppressed.

Hereinafter, the present invention will be described in more detail.
As shown in FIG. 4 (a), in the press bending method of the present invention in which the restraint of the bent portion of the metal pipe to be processed is supported at four points, the bending mold, the cushion mold, and the two movable rolls Use a mold. These dies are preferably formed with grooves having a short semicircular cross section that is equal to or less than the semicircular arc of the metal pipe to be processed. For the power of the mold, a hydraulic cylinder or an air cylinder is used so that a load can be applied to the metal pipe. A load in the direction perpendicular to the metal pipe to be processed is applied to the bending mold and the cushion mold, and a load is applied to the movable roll in the pipe axis direction. The mobile roll may be rotatable or may not be rotated.

  As shown in FIG. 4B, in a state where the metal pipe to be processed is placed on the cushion mold, bending is performed by pressing the bending mold against the metal pipe and the cushion mold. At that time, since the rolls that move in the left-right direction of the tube axis are attached to both ends of the cushion mold, the left and right mobile rolls move left and right along the bending mold as the bending mold is pushed. The metal tube is bent. At this time, the movable roll and the cushion mold can adjust the load applied to the metal pipe by using a cylinder or a spring using hydraulic pressure or air.

In the press bending method, the bending stress at the bending center becomes the largest at the initial bending stage where the bending angle θ is 0 <θ ≦ 30 °, and buckling is likely to occur. For this reason, as shown in FIG. 5, at the initial stage of bending when the bending angle θ is 0 <θ ≦ 30 °, the frictional force F on the outer surface of the pipe due to the cushion load and the roll load is provided by providing a cushion mold at the center of bending. Bending is performed while tension is generated from ₁ and F _{2 at} the bent portion of the metal tube, and the compressive stress at the bending center is relaxed, thereby suppressing the occurrence of buckling.

  When the bending angle θ is 30 ° or more, the bending process at the bending center is completed because the bending process at the bending center has been completed, and the bending center can be processed without buckling. (See FIG. 4C). Thereby, the bending stress generated in the bending portion is in a state of being reduced as a whole. For this reason, by bending the bending mold while the metal pipe is restrained by the bending mold and the cushion mold, it is possible to perform bending without buckling while the mobile roll presses the metal pipe along the bending mold. It becomes.

In addition, it is preferable that a groove | channel is provided in a contact surface with a to-be-processed metal pipe, and the cross-sectional shape of the groove | channel is made into a semicircle shape shorter than the semicircle of a to-be-processed metal pipe in a movable roll and a cushion metal mold | die. With such a sectional shape, it is possible to increase the axial compression tension frictional force F ₁ and F ₂ is increased metal tube in the processed metal tube outer surface, as a result, the suppression of buckling The effect can be further increased.
Further, by bending by placing a restraining material such as sand, beads or steel shot in the metal tube, the rigidity of the bent portion of the metal tube is increased, and buckling and flatness can be further suppressed.

Next, a case where the bending method of the present invention is experimentally introduced will be introduced.
A ferritic stainless steel pipe was used as the material.
Table 1 shows the dimensions and mechanical properties of the ferritic stainless steel pipe. A small diameter thin tube having a t of 0.8 mm or less and a t / D of 5.0% or less was used.
Table 2 shows the bending conditions during processing. Bending with a small bending center radius (R / D is 3 or less) by using three types of bending center radius R: 56mm (3.5D), 24mm (1.5D), 16mm (1.0D) It was. The set bending angle was 90 °, and there were two types of restraint using sand from inside the steel pipe and no restraint.

  FIG. 6 shows a press bending method using a movable roll and a mold shape used. FIG. 6A shows a schematic diagram of a press bending method using a movable roll. The movable roll has a structure capable of applying a load, and the cushion mold has a structure capable of applying a load by using a cushion spring. As shown in FIG. 6B, the bending mold, the movable roll, and the cushion mold have a groove shape, where the groove width is W, the groove height is H, and the groove radius is r.

Furthermore, it shows about the metal mold | die conditions at the time of the process used for Table 3. The unit of the numerical value indicating the groove shape in Table 3 is mm. The roll load was set to a constant value of 0.4 MPa.
Comparative Examples 1 and 2 are press bending methods using a three-point support, which is a conventional press bending method, and Examples 1 to 8 are press bending methods using a four-point support. The groove shape of the bending mold and the cushion mold is the groove width W16 × groove height H8 × groove radius r8 in Comparative Examples 1 and 2 and Examples 1 to 8, and the roll groove shape is the groove width in Examples 1 to 4. W16 × groove height H8 × groove radius r8. In Examples 5 to 8 and Comparative Examples 1 and 2, the groove width was W16 × groove height H8 × groove radius r7.5. The cushion spring constant is 100 N / mm in Examples 1, 2, 5, and 6, and 25 N / mm in Examples 3, 4, 7, and 8. As for the restraint in the steel pipe, sand was used in Examples 1, 3, 5 and 7 and Comparative Example 1, and no restraint was used in Examples 2, 4, 6, 8 and Comparative Example 2.

Table 4 shows the results of this processing test example.
In the conventional press bending method with the three-point support of Comparative Examples 1 and 2, buckling occurs in any processing condition regardless of whether sand is put in the steel pipe or not. It turned out that a small bending process (R / D is 3 or less) and a bending process are difficult.
In Example 1 using the press bending method with four-point support, the bending center radius is 56 mm (3.5 D), the plate thickness of the steel pipe is 0.4 mm to 0.8 mm, and the bending center radius is 24 mm (1.5 D). Bending without buckling was possible under the processing conditions where the steel pipe thickness was 0.6mm to 0.8mm, the bending center radius was 16mm (1.0D), and the steel pipe thickness was 0.8mm. At 24 mm (1.5 D), the steel pipe thickness was 0.4 mm, the bending center radius was 16 mm (1.0 D), and the steel pipe thickness was 0.4 mm to 0.6 mm, buckling occurred. From this result, bending center radius R became small, and bending forming became difficult because thickness reduction of the steel pipe plate thickness progressed.

In the condition where sand is not put in the steel pipe of Example 2 (other conditions are the same as in Example 1), the processing conditions with a bending center radius of 56 mm and 24 mm (1.5 D) are the same as in Example 1. However, when the radius of bending center was 16 mm (1.0 D), buckling occurred when the plate thickness of the steel pipe was 0.4 mm to 0.8 mm. From this result, under the condition where sand is not put into the steel pipe, since the restraint in the steel pipe is lost, buckling is likely to occur and the forming range is narrowed.
In the condition where the cushion spring constant of Example 3 is 25 N / mm (other conditions are the same as in Example 1), the same molding as in Example 1 is performed under the processing conditions where the bending center radius is 56 mm and 24 mm (1.5 D). However, when the bending center radius was 16 mm (1.0 D), buckling occurred when the steel pipe plate thickness was 0.4 mm to 0.8 mm. From this result, when the cushion spring constant was low, the cushion load was reduced, buckling was likely to occur, and the molding range was narrowed.

In the condition where sand was not put into the steel pipe of Example 4 (other conditions were the same as in Example 2), the same formability as in Example 1 was obtained in the processing condition with a bending center radius of 56 mm (3.5 D). However, if the bending center radius is 24mm (1.5D), the steel pipe can only be formed with a thickness of 0.8mm, buckling occurs between 0.4mm and 0.6mm, and if the bending center radius is 16mm (1.0D), Buckling occurred when the plate thickness was 0.4mm to 0.8mm. In Example 4, sand was not put in the steel pipe, so the molding range was narrower than that in Example 3.
From the results of Examples 1 to 4, the bending center radius is 24 mm (1.5 D), the steel pipe thickness is 0.4 mm, the bending center radius is 16 mm (1.0 D), and the steel pipe thickness is 0.4 mm to 0.8 mm. Buckling occurred under the processing conditions. Therefore, based on these results, in Examples 5 to 8, experiments were performed with the groove radius of the roll groove shape being reduced to 7.5 mm. The conditions other than the change of the roll groove shape are the same as those in Example 1, Example 6, Example 2 in Example 5, Example 7 in Example 7, and Example 3 in Example 8.

From the results of Examples 5 to 8, the bending forming range was wider than the results of Examples 1 to 4 by reducing the groove radius of the roll groove shape to 7.5 mm. In Example 5, the cushion spring constant is 100 N / mm, sand is put in the steel pipe, the bending center radius is 24 mm (1.5 D), the steel pipe sheet thickness is 0.4 mm, and the bending center radius is 16 mm (1.0 D). ) Makes it possible to bend the steel tube with a processing thickness of 0.6 mm to 0.8 mm.
From the above, it was found that buckling can be further suppressed by making the groove cross-sectional shape of the roll into a semicircular shape shorter than the semicircle of the steel pipe.

Claims (5)

  A metal pipe to be processed is placed on a cushion mold and a pair of movable rolls arranged on both sides thereof, and the bending metal mold is pressed against the metal pipe to be processed from directly above the cushion mold. Metal tube bending method.   The method for bending a metal tube according to claim 1, wherein a load for restraining or bending the metal tube to be processed is applied to each of the bending die, the cushion die, and the pair of movable rolls.   A bending die, a cushion die having a semicircular cross-sectional groove having a width equal to or larger than the diameter of the metal pipe to be processed and a depth equal to or larger than the radius of the metal pipe to be processed on each of the metal pipe contact surfaces. The method for bending a metal pipe according to claim 1 or 2, wherein a pair of movable rolls is used.   A bending die, a cushion die, and a pair of mobile rolls are used in which the arc length of the groove portion combining the bending die and the cushion die and / or the bending die and the movable roll is equal to or less than the circumference of the metal tube. The method for bending a metal tube according to claim 3.   5. The bending process according to claim 1, wherein bending is performed with a restraint material such as steel shot, sand, or beads inserted in the metal pipe as a wrinkle suppression method according to the processing conditions of the dimension of the metal pipe and the bending center radius. The bending method of the metal pipe as described in 2.

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